Foldable beds, and particularly those folding beds which are stored within other furniture items, are an attractive bedding option for consumers with restricted living space. Typically a foldable bed folds upon itself either one or two times for easy storage, then unfolds into a bed for sleeping. The bed generally includes a mattress that is sufficiently flexible to fold upon itself and a frame which serves as both the supporting bed frame and a restraining unit for the mattress in its folded position. The frame includes a body section pivotally attached at one end to the end of an intermediate cavity section, the opposite end of which is attached to a seat section; these sections are serially aligned horizontally in the unfolded position, and are folded back upon one another such that the body section and seat section are substantially parallel to one another and are perpendicular to the cavity section. The frame is often mounted in an upholstered sofa or chair frame into which the bed frame and mattress are folded and stored when not in use. Cushions are then placed upon the folded mattress for use of the unit as a sofa or chair.
To date, foldable beds have exhibited a number of shortcomings. One general area of dissatisfaction is the sleeping comfort of the bed. For storage purposes, it is desirable that the mattress fold into the thinnest package possible. The need for a compactly folded mattress is particularly important if the mattress and frame are attached to a sofa or chair, since the mattress and frame must fit within the walls of the sofa or chair, which likely has style or ergonomic restrictions. Thick, firm mattresses that would provide suitable sleeping comfort are too bulky to be folded into the space available in many sofa or chair styles; in particular, transitional and contemporary styles often have either a low seat height or an "off-the-floor" front profile and thereby have limited space available in which to store a bed. Present sofas have addressed the size constraint by employing a mattress that is either thin and easily folded into a thin unit, soft and easily crushed, or a combination of each. The result of such compromises is often an unsatisfactory sleeping surface.
Attempts have been made to address the aforementioned problem. One solution has been the development of "collapsible" springs that comprise some or all of the supporting springs in the mattress. These springs are generally planar and are pivotally interconnected at each end to a pair of wire grids that are adjacent and parallel with the upper and lower upholstery faces of the mattress. The springs are oriented to be parallel with the head and foot end faces of the mattress and orthogonal to the upper, lower, and lateral faces of the mattress. When the bed is in its unfolded position, the springs are upright. However, as the bed moves to its folded position, the springs pivot about the wires comprising the grid so that the mattress upper surface is drawn closer and shifts longitudinally relative to the mattress lower surface. As a result, the distance between the upper and lower mattress surfaces (i.e., the thickness of the mattress) is significantly decreased, thereby giving the mattress the appearance of having "collapsed". Examples of collapsible springs suitable for use in foldable bedding are illustrated in Miller U.S. Pat. Nos. 4,489,450, 4,620,336, 4,654,905, and 5,184,809 and Rogers U.S. Pat. No. 5,257,424.
One particular shortcoming of beds having collapsible springs has been the expense of production. Their cost has been quite high because, to date, special machinery has been required to produce these springs. This is particularly true for "M-shaped" springs of the type illustrated in, for example, Miller U.S. Patent No. 4,654,905; Miller U.S. Pat. No. 5,184,809.
In addition, collapsible springs have encountered difficulty with "overrotation" when in the upright position. More specifically, the springs have a tendency to rotate beyond their upright position, particularly if the mattress is under a compressive load. Unless such rotation is halted by somehow constraining the entire mattress section to another mattress section or to the bed frame, the mattress upper surface shifts longitudinally relative to the mattress lower surface, thereby causing the mattress thickness to diminish.
Further, because of their generally planar configuration, collapsible springs are often limited in the degree to which they can be compressed. For example, a sinuous spring such as that illustrated in Miller U.S. Pat. No. 4,654,905 can compress within its plane only until adjacent undulations contact one another. This problem is not present in coiled springs, as their general shape precludes contact between adjacent coils due to compression until the spring is compressed to a far greater degree than a typical occupant would induce. Limited compression of collapsible springs can render them less comfortable for sleeping; if the occupant is positioned so that a spring is fully compressed, that spring will provide an unforgiving location on the mattress, thus causing the mattress to have inconsistent firmness. In addition, contact between adjacent undulations of sinuous springs under compression can cause a mattress to be somewhat noisy, which, of course, is quite undesirable for a sleeping occupant.
The grid wires comprising the grid to which the springs are attached also present problems. The springs are generally attached to the grid wires either by a clip that encircles the grid wire and spring run, or by a helical wire. For ease of production and for cost reasons, interconnection with a helical wire is preferred; however, previous attempts to interconnect grid wires and spring runs have not been entirely successful; The grid wires, which extend longitudinally (i.e., from head to foot), include perpendicularly-extending finger portions that have at their ends a small loop that extends toward the foot end of the bed. Bed stability improves as the diameter of the helix decreases, so it is desirable to use the smallest possible helix. In many prior embodiments, the helical coil is threaded through the loop in the grid wire. This is a relatively precise task that can be difficult to perform repeatedly with automated equipment. Also, because all of the finger portions extend toward the foot end of the bed, each grid wire must be manufactured separately rather than being able to "double-back" on itself to form the adjacent grid wire. Accordingly, it would be desirable to provide a grid wire configuration that is more conducive to automated assembly with a helical wire and that can be used for multiple adjacent grid wires.
The use of collapsible springs also complicates the folding of the mattress. Because the upper and lower mattress surfaces have shifted relative to one another in the folded position, the mattress length must be reduced in order for the mattress to fold upon itself and fit within the cavity of the seating unit. One approach, illustrated in Rogers U.S. Pat. No. 5,257,424, is to add an additional pivoting section to the mattress at the foot end of the seat section. This approach requires, of course, that the frame and the mechanism controlling the movement thereof have configurations that differ from those used with conventional mattresses.
In view of the foregoing, it is an object of the present invention to provide a foldable bed that includes collapsible springs but that utilizes relatively inexpensive materials and assembly methods.
It is also an object of the present invention to provide a collapsible spring, and in particular a collapsible sinuous spring, that can be compressed to a greater depth than is available for prior art springs.
It is a further object of the present invention to provide a mattress having collapsible springs that do not "over-rotate" from the upright position.
It is an additional object of the present invention to provide a grid wire to be used with collapsible springs that can be easily interconnected therewith with helical wires via automated equipment.
It is another object of the present invention to provide a foldable bed having collapsible springs that can utilize modified conventional bed frame configurations.
It is a further object of the present invention to provide a foldable bed that can be used with a mattress of standard length without major modification of existing bed frames and folding mechanisms.